Research On The Control Techniques Of Convex Cracking And Warping Springback Caused By Local Features Forming During The Large Sheet Parts Stamping Process

Large scale sheet metal stamping parts, such as baseplate, back panel, matrix parts,are very widely used in the automotive industry and household electrical applianceindustries. The characteristic of these parts is thin thickness (0.6~0.8mm), large sizeand poor stiffness. And they are composed of the local features which are nonuniformdistribution and different depths. Due to the uneven forming of the local features, thecomplex large sheet metal stamping parts often occur convex cracking, light wrinklingof large area and overall warping springback. These defects seriously affect the productquality and the accuracy of the assembly, and extend the upgrade cycle of the product.Since the1990s, a large number of researchers did much research about thecracking problem. Generally, cracking problem can be solved well by adjusting theBHF and setting drawbeads. But for some special parts, such as back panel, the BHFcan not be adjusted during the stamping process. For the cracking problem of this kindof parts, new solutions need to be found. About the springback prediction and controlproblem, many researchers did much works in the recent years. But the study workabout the warping springback caused by local features forming is relatively few. And atpresent, it is very lack of practical methods and processes for the warping springbackcontrol.Based on engineering practice, the finite element numerical simulation method isused in this paper to find the solutions to the convex cracking and warping springbackproblem caused by local features forming during the large sheet parts stampingprocess.The main content of this paper is as below:(1) Based on the analysis of the structure and forming characteristics of the backpanel parts, the reasons and mechanisms of the warping springback problem areexplained. This paper considers that the unstability caused by the releasing of thealternative distribution of the tensile and compressive stress and the residual moment isthe root reason of the warping springback problem.(2) The multi-step forming method is proposed to solve the bottom crackingproblem of the rectangular convex during the back panel stamping process. In order toget better forming quality, the quality function of the SECCN5is established and theadaptive response surface method is used to optimize the geometric parameters (die entrance fillet radius R1, punch fillet radius R2, forming depth H) of the intermediateconfiguration.(3) The warping springback control method based on the local features isinvestigated in this paper. The method of feature extraction is used to extract a small Ltype feature from the back panel parts. The moment-counterbalanced method andwave-cutting method are proposed to solve the warping springback problem andwork very well in the control of the warping springback problem which occurs in thesingle feature and multiple features forming process, thus can be used to control thewarping springback problem during the back panel stamping process.(4) The warping springback control method based on the integral stiffness isstudied in this paper. The topography optimization method is used to design the layoutof the strengthened imprint. The strengthened imprint layout is designed in theundeformed region of a typical back panel parts by the topography optimizationmethod and the engineering manufacturing treatment is applied on the optimizationresult. The computation result shows that every non-rigid body order modal naturalfrequency has a great improvement, and the integral stiffness of the back panel issignificantly enhanced. Thus, this method can be used to control the warpingspringback problem.